It has been common practice in this art to support the drive wheels with a dead axle in the form of a housing extending transversely of the vehicle and through which extend live axle shafts connecting the wheels to differential gearing within an enlarged central portion of this housing. The vehicle body or frame (in the case where the body and frame are fabricated other than as a single unit) rests on springs which are supported by this axle housing a short distance inboard of each wheel, and the wheel brakes are interposed between the wheels and the springs.
Although this long-used standard type axle has advantages of ruggedness and simplicity of design, it also suffers from numerous disadvantages, chief among which are that vehicle loading is restricted by the necessity of maintaining vertical clearance between the body understructure and the differential and the fact that the differential, pinion and ring gear assembly, as well as all of the dead axle housing and of the live axles and a portion of the weight of the drive shaft from engine to the differential all contribute to the unsprung weight of the vehicle. While efforts have been made to eliminate this problem by mounting the differential to the vehicle body and using universal joints in the live axles, they have all entailed wheel supporting schemes that were deficient in ruggedness, simplicity of design, and cost for use in heavier trucks and buses.
As representative of such prior designs in which the differential is body-mounted are those wherein the wheel movements are controlled by a parallel arm type suspension as shown in U.S. Pat. No. 2,067,807 to Williams, by a wish-bone type suspension as shown in U.S. Pat. No. 2,988,161 to Herr, by a cross-beam pivotally connected to the wheel spindles as shown in U.S. Pat. No. 3,356,176 to Herr, by swinging half-axles shown in U.S. Pat. No. 2,675,085, and by a bowed dead axle as shown in U.S. Pat. No. 562,289 to De Dion et al.
The latter, De Dion type, suspension, of which later U.S. Pat. Nos. 2,716,461 to MacPherson, 2,753,190 to Hooven and 3,373,834 to Rosenkrands represent modifications, has the advantage of retaining a dead axle with rigid connections to the wheel bearing support members. Since the dead axle is bowed in the horizontal plane to clear the differential housing, it also contributes to lowering the vehicle body height (or increasing the payload) since limits on minimum body height are not dependent on maintaining vertical clearance thereof with the differential housing.
A serious drawback to the De Dion arrangement, however, and which has precluded its use on the heavier trucks and buses, is that the bowed configuration of the dead axle results in it being subjected to torsional stress in resisting relative vertical displacement of the left and right road wheels connected to it. Any significant torsional deflection of this dead axle would produce undesirable movements of the wheel axes, and the necessary torsional stiffening to avoid this so increases the weight and size of the axle as to make its use prohibitive from a cost and design standpoint.
My invention enables obtaining all the advantages of reduced unsprung weight, etc. from mounting the differential to the vehicle body, as well as the additional advantages of rigid support of the wheel bearings and vertical freedom of movement of the De Dion dead axle, without the undesirable torsional stressing inherent in the latter. I accomplish this by providing a rack-type dead axle having two generally straight cross-members which span the differential and ring gear housing and whose ends are rigidly interconnected by longitudinally extending members which constitute the bearing supports for the road wheels. The nearest similar arrangement of which I am aware is the dead axle in U.S. Pat. No. 2,132,983 to Nallinger which is bowed to clear the body-mounted differential, but is held in position by a system of spring biased rollers and a long forwardly extending wishbone pivoted to the body at its front end.
I am also aware that a rack-type dead axle in the form of an open rectangular or box-like frame is not new per se, being shown in U.S. Pat. Nos. 1,479,187 to Lansden, 2,410,133 to Spatta, and 3,896,895 to Schultz et al, for example. In all such prior art of which I am aware, however, its advantages in combination with a body-mounted differential have not been suggested or appreciated.